1. Field of the Invention
The present invention relates to an optical element covering member, a backlight provided with the optical element covering member, and a liquid crystal display device. In particular, the present invention relates to an optical element covering member for improving display characteristics of a liquid crystal display device.
2. Description of the Related Art
In liquid crystal display devices, many optical elements have been used previously for the purpose of improving the viewing angle, the luminance, and the like. As for these optical element, elements in the shape of a film or a sheet, e.g., diffusion films and prism sheets, have been used.
FIG. 1 shows the configuration of a liquid crystal display device according to a related art. As shown in FIG. 1, this liquid crystal display device is provided with an illumination device 101 for emitting light, a diffusion plate 102 for diffusing the light emitted from the illumination device 101, and a plurality of optical elements 103, for example, for collecting or diffusing the light diffused by the diffusion plate 102, and a liquid crystal panel 104.
There are tendencies of the self weight and the size of an optical element to increase with upsizing of an image display device in recent years. If the self weight and the size of the optical element increase, the rigidity of the optical element becomes insufficient and, thereby, deformation, e.g., wrinkling, bending, or warping, of the optical element occurs. Such deformation of the optical element exerts an influence on the optical directivity toward a display surface so as to cause a serious luminance irregularity problem.
Consequently, it has been proposed that the insufficiency in rigidity of the optical element is improved by increasing the thickness of the optical element. However, the liquid crystal display device becomes thick and, thereby, advantages of the liquid crystal display device in being low-profile and lightweight are impaired. Then, it has been proposed that the insufficiency in rigidity of the optical element in the shape of a sheet or a form is improved by bonding optical elements to each other with a transparent adhesive (refer to Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-301147, for example).
Furthermore, since the application range of display devices has been extended in recent years, further thickness reduction and weight reduction have been proposed for the purpose of wall-mounting or installation in the vicinity of a ceiling. Regarding this thickness reduction and weight reduction, a diffusion function for equalizing irregularity in light source, e.g., fluorescent tubes, does not accompany. Therefore, technologies for reducing irregularity in light source by increasing the thickness of the diffusion plate, using a plurality of diffusion sheets, i.e. increasing the number of sheets than ever, increasing the number of light sources, and the like have been studied.